The human pituitary proteome includes all proteins that are expressed in the given time. Unlike a genome, the proteome is not fixed, but it changes depending on the conditions. Proteome science (proteomics) employs a combination of state-of-the-art separation techniques, mass spectrometry, and bioinformatics for the study of proteomes. A promising prospect is the application of proteome research for the investigation of tumor pathologies. Qualitative and quantitative changes in the proteome that are associated with tumor formation can be monitored by a comparison of healthy (control) vs. tumor tissue, and the proteins of interest can be characterized, Here, the proteomics approach will be applied to the study of the proteome in human pituitary macroadenomas (hormonally silent tumors). The objective of the proposed research program is to generate a two-dimensional reference map of human pituitary proteins, and to characterize the proteins whose expression is modified in pituitary macroadenomas. The proteins will be separated by two-dimensional gel electrophoresis, and the 2D maps will be digitized. 2D gel images from control versus tumor proteomes will be compared, and protein spots will be quantified. The proteins whose abundance is altered in pituitary tumors will be identified and characterized. The protein of interest will be digested, and the masses of the resulting peptides will be measured by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Amino acid sequence of the peptides will be determined by electrospray-ion trap mass spectrometry. Using these peptide-mapping and/or sequencing data, the protein will be identified by searching a protein sequence database. Characterization of differentially expressed pituitary proteins will also include a detailed investigation of changes in posttranslational protein modifications. In addition, a number of prominent proteins from the control pituitary proteome will also be characterized, and a 2D reference database of the human pituitary will be constructed. Knowledge of the changes in protein expression in pituitary macroadenomas will help clarify fundamental mechanisms of macroadenoma formation, which may lead to the development of more effective means to treat and manage these tumors.